A large number of volatile inhalants are deliberately inhaled, presumably for their intoxicating effects. Few studies, though, have systematically examined the behavioral effects of inhalants which are related to their abuse. A series of experiments are proposed in this application to examine the subjective and reinforcing (rewarding) effects of a commonly-abused inhalant, nitrous oxide, in healthy volunteers. In the first study, the mood-altering and psychomotor effects of several subanesthetic concentrations of nitrous oxide will be tested in healthy volunteers. In the second study, a preference procedure will be used to assess the reinforcing effects of nitrous oxide: subjects will inhale nitrous oxide and oxygen during sampling sessions, and then during subsequent choice sessions will choose which agent to inhale. In the third study, healthy volunteers will inhale subanesthetic concentrations of nitrous oxide, isoflurane and enflurane in order to determine if these inhaled general anesthetics have a similar spectrum of subjective effects. In the fourth and fifth studies, the subjective effects of nitrous oxide will be compared to CNS depressants and opiates - data form other behavioral preparations suggest that nitrous oxide, barbiturates, ethanol, and opiates may share a common spectrum of subjective effects. These studies will serve as an initial step in developing a model for studying the behavioral effects of inhalants which contribute to their abuse.